REPRESSION OF LIPOPOLYSACCHARIDE BIOSYNTHESIS IN ESCHERICHIA-COLI BY AN ANTISENSE RNA OF ACETOBACTER-METHANOLICUS PHAGE ACM1

Lysogenic Acetobacter methanolicus strains carrying the prophage Acm1 were found to be unable to synthesize both the capsular polysaccharide (CPS) and the O-specific side-chain of lipopolysaccharide (LPS) and t o represent rough variants of the host bacterium, A 262 bp DNA fragmen t of phage Acm1, obviously required for interference with LPS biosynth esis, was cloned and expressed in Escherichia coli, Independently of t he O-type, transformation of various E. coli strains with the recombin ant DNA resulted in a suppression of biosynthesis of the O-specific ch ains. The DNA fragment of phage Acm1 contained three very short open r eading frames of 21, 24, and 36 bp, However, attempts to express phage -encoded peptides were not successful, Instead, the Acm1-derived DNA f ragment was shown to code for the synthesis of a trans-acting RNA mole cule of 97 nucleotides, designated lbi (LPS biosynthesis-interfering) RNA, This RNA contains sequence complementarity to E. coli target RNA sequences and appears to have the ability to form intracellularly RNA hybrid duplexes with mRNA, The data presented in this study support th e hypothesis that the phenotypic effect of conversion to rough-type LP S is accompanied by the expression of an antisense RNA of phage Acm1.